Embodiments of the invention relate generally to drive systems and, more specifically, to selectively coupling an energy source to a load to supply energy thereto in a vehicle or non-vehicle system.
Electric vehicles and hybrid electric vehicles are typically powered by one or more energy storage devices, either alone or in combination with an internal combustion engine. In pure electric vehicles, the one or more energy storage devices powers the entire drive system, thereby eliminating the need for an internal combustion engine. Hybrid electric vehicles, on the other hand, include energy storage device power to supplement power supplied by an internal combustion engine, which greatly increases the fuel efficiency of the internal combustion engine and of the vehicle. Traditionally, the energy storage devices in electric or hybrid electric propulsion systems include batteries, ultracapacitors, flywheels, or a combination of these elements in order to provide sufficient energy to power an electric motor.
When two or more energy sources are used to provide power to drive system, the energy sources are typically well-suited to provide different types of power. A first energy source, for example, may be a high specific energy source that is more efficient or economical at providing long-term power while a second energy source may be a high specific-power source more efficient at providing short-term power. The high specific-power source may be used to assist the high specific energy source in providing power to the system during, for example, acceleration or pulsed load events.
Often, the high specific-power source is directly coupled to the direct current (DC) link that supplies a voltage to a load. However, control of the DC link voltage is dependent on the directly coupled high power source and can be lower than a desired response. In addition, the transient power required from the high energy source to be supplied to the DC link can be higher than a desired response.
Therefore, it is desirable to provide a system that allows selective coupling of an energy source to a load to supply energy thereto.